1. Field of the Invention
The present disclosure generally concerns drilling rig and mobile well servicing rig braking systems. More specifically the present disclosure concerns improved linkage assemblies for a drilling or mobile well servicing rig braking system, and drilling or mobile well servicing rig braking systems comprising such improved linkage assemblies.
2. Description of the Related Art
Drilling rigs and mobile well servicing rigs generally include a manual braking system to allow the operator to control the position of the traveling blocks, and additionally are often equipped with an emergency brake safety system that prevents or a least reduces the possibility of the traveling blocks from reaching a crown out or floor out position. The techniques to actuate the emergency brake and prevent crown outs and floor outs can vary. These techniques include use of wire trip sensors, radar, ultrasonic sensors located near the crown, drum encoders, and wire rope counters as sensing devices that determine if the blocks are too close to the crown. In addition, the emergency brake safety system may incorporate programmable logic control circuits to detect and actuate cylinders. In another embodiment, the emergency brake safety system can be configured in a “fail safe” mode. When a circuit is broken in the fail safe mode, a cylinder is activated, thereby activating the braking system on the hoist to prevent the drilling line from additional movement.
While many different methods exist for preventing crown outs and floor outs, most have a single commonality, that being when a sensor or other device detects the pending crown out or floor out, the device sets the brakes for the tubing drum via a pneumatic or hydraulic cylinder. U.S. Pat. No. 7,513,338 (“the '338 patent), incorporated herein by reference in its entirety, describes a conventional tubing drum brake assembly (see FIG. 1 of the '338 patent). As shown in FIG. 1 of the '338 patent, the brake bands are actuated by the equalizer bar rotating in the clockwise direction, which generates tension on the brake bands, causing them to tighten up and apply pressure to the brake flanges. The pressure applied by the brake bands causes the tubing drum to slow or stop its rotation about the tubing core depending on the amount of pressure applied by the brake bands and causing a corresponding reduction in movement of the feed line (see FIGS. 1-4 of the '338 patent).
As further shown in FIG. 1 of the '338 patent, a conventional braking system can rotate the equalizing bar by applying a downward force on a brake handle. The brake handle is attached to a brake lever, which rotates about a pivot point when the downward force is applied to the brake handle. The rotation of the brake lever rotates a bell crank in a clockwise direction, the bell crank and brake lever being mechanically coupled to one another. The bell crank is attached at one end to the brake lever and attached at another end to the brake linkage and rotates about the pivot point. The brake linkage is attached at the other end to the equalizer bar. The rotation of the bell crank creates a tension in the brake linkage, thereby causing the equalizer bar to rotate in the clockwise direction about a pivot point on the equalizer bar.
In order to effect the safe braking of the rig or hoist, the braking system must operate under tight tolerances, which necessitates that the brake bands remain in constant or virtually constant contact with the brake flanges. Because the weight of the brake handle and brake lever will provide sufficient down force to slow the rotation of the drum, the operator typically will lift up on the brake handle and lever (see FIG. 2 and FIG. 3 of the '338 patent). By lifting the brake handle and lever, the brake bands provide less pressure on the brake flanges, thereby allowing the drum to rotate at a higher rate of speed.
As discussed above and shown in greater detail in FIG. 4 and FIG. 5 of the '338 patent, most conventional rig braking systems include an emergency brake safety system to prevent a crown out or floor out event. The emergency brake generally includes a cylinder that can be pneumatically or hydraulically operated. When activated, the cylinder suddenly extends a piston rod or shaft outward and provides pressure on a lever that is attached to the equalizer bar. In response to the pressure, the equalizer bar rotates clockwise causing the brake bands to apply pressure to the brake flange, thereby slowing the drum and the feed line. However, because the equalizer bar is also mechanically linked to the brake handle via the brake linkage, bell crank, and brake lever, the brake handle suddenly moves in the downward direction in response to the actuation of the cylinder. If the rig operator is in the vicinity of, or is holding the brake handle up to reduce braking pressure on the drum, actuation of the cylinder may cause injury to the operator due to the sudden and forceful downward movement of the brake handle.
To address this problem, the '338 patent discloses the use of a spring to connect the brake handle and the bell crank. However, this arrangement still transmits considerable movement and force to the brake handle upon actuation of the emergency brake, potentially injuring the operator.
Therefore, there is a need in the art for a braking system that allows the emergency brake cylinder to act independently of the brake handle, so when the emergency brake cylinder is actuated due to the detection of a crown out, floor out or other action or problem, the brake handle will not react suddenly and violently and potentially cause injury to the operator.